Phase transformations in the KNd(SO<sub>4</sub>)<sub>2</sub> ∙ H<sub>2</sub>O–SrSO<sub>4</sub> ∙ 0.5H<sub>2</sub&

X-ray phase and thermogravimetric analysis methods established the existence of 3 crystalline hydrate modifications, having the composition KNd(SO4)2 ∙ H2O and parameters of their elementary cells are defined. Dehydration in the heating process of KNd(SO4)2 ∙ H2O at a temperature of 250°C leads to the formation of a partially dehydrated modification of the approximate composition of KNd(SO4)2 ∙ 0.2H2O. Further heating to 400°C completes the complete dehydration with formation of the anhydrous monoclinic modification KNd(SO4)2. The high-temperature triclinic modification KNd(SO4)2 exists in the temperature range 635–900°C and decomposes when heated above 900°C. The trigonal modification KNd(SO4)2 forms solid solutions with the crystalline matrix SrSO4 ∙ 0.5H2O. The anhydrous modification KNd(SO4)2 does not form solid solutions with the anhydrous rhombus modification SrSO4∙